Linear actuator primarily uses driving components such as a motor, a worm and a worm wheel to drive a lead screw rod, while using the lead screw rod to drive a telescopic pipe installed to the lead screw rod for a linear extension or retraction movement. Since the structure and installation of the linear actuator are simpler and easier than those of pneumatic and hydraulic cylinders, the linear actuator has been used extensively in various equipments such as hospital beds and electric chairs or in any other areas that require extension and retraction operations.
In the conventional linear actuators as disclosed in European Patent Publication No. EP0662573B1 and PCT Publication No. WO2004-027290A2, the linear actuator disclosed in EP0662573B1 comprises: a worm; a lead screw rod; a worm wheel module fixed to an end of the lead screw rod and including a worm wheel; and a torsion spring installed around the external periphery of a cylindrical annulus. In WO2004-027290A2, a thermal conductive element is provided for dissipating heat generated by frictions during the operation of the torsion spring with the annulus.
However, the torsion spring of the conventional linear actuator is fixed, and the cylindrical annulus rotates with the worm wheel, so that heat is generated by frictions produced between the torsion spring and the cylindrical annulus, usually made from plastic and the heat may melt or damage the cylindrical annulus easily, thus reducing the service life significantly. Further, only the linear contact between the torsion spring and the rotating cylindrical annulus is provided for a braking effect or a speed reduction effect, but such a braking effect or a speed reduction effect is limited because the effective contact area between the torsion spring and the ring is small.
In view of the aforementioned drawbacks of the prior art, the inventor of the present invention based on years of experience in the related industry to conduct extensive researches and experiments, and finally provided a feasible solution in accordance with the present invention to overcome the drawbacks of the prior art.